The invention relates to metallurgy in general and more particularly to a method for joining bodies made by powder metallurgy to compact bodies by compound sintering, and to the application of this method to the joining of pressed bodies of steel bonded hard material, especially a metal carbide, and preferably titanium carbide, to steel.
It is an object of the present invention to describe a method which is as economical, i.e., as cost-effective as possible, and with which it is possible to pair a tough, solid, compact base body, for instance, of steel, with a highly wear-resistance body made by powder metallurgy. Generally, highly wear-resistant materials have too high a content of hard materials (metal nitrides, borides, silicides and carbides) that they cannot be produced by melting metallurgy. They are therefore produced by powder metallurgy, the hard material component in powder form being mixed, pressed and sintered with a metallic binder, likewise in powder form.
Methods for joining of compact bodies of the same or different composition are known in the art. "Industrie-Anzeiger" 1968, pages 18 to 23, generally teaches joining by pressure welding. This is carried out by heating up the bodies to be joined together, compression with low pressure without deformation, and sintering together in a vacuum or in a protective gas, optionally with metallic intermediate layers (diffusion welding). The sintering together of two pressed bodies or two sintered bodies, optionally with powdering the contact surfaces with a material of high vapor pressure, is described in German Pat. No. 867 164. Placing pressed or sintered bodies on top of one another after first machining the contact surfaces by chip removing methods and sintering together is disclosed in German Auslegeschrift No. 14 71 078.
It is a common feature of all these known methods that their objective is only the joining of similar bodies. Therefore, either pressed bodies are joined together or sintered or solid bodies are joined. The sintering together of bodies with different starting structure, i.e., for instance, pressed bodies to sintered bodies or pressed bodies to solid bodies has been performed heretofore only after hot pressing. In this case, a bed of powder or a pre-pressed body is placed on the compact, i.e., solid, base body, and the former is then pressed against the compact body at high pressure and high temperature. Subsequently, the compound sintering is performed. While this hot pressing leads technically to a usable product, it has the disadvantage that it requires a large amount of equipment and energy for generating the pressure and the temperature and is therefore very expensive.
Another method is known (German Pat. No. 21 39 738), by which a compound body can be produced from two different materials in such a manner that a bed of the different powders is prepared in two layers; these are then pressed and subsequently sintered. This method, however, only makes possible the fabrication of a power metallurgy compound product, but not the joining of a power metallurgy product to a compact body.